In the technical field of the manufacture of integrated circuits, especially of MOS transistors, it is increasingly necessary to stabilise the physico-chemical properties of the various zones of these integrated circuits, especially at the level of the metal contact/semiconductor material interfaces.
Among recent developments in this technical field, it has been proposed to use, as contact metal, intended for providing the electrical contacts with the source, gate and drain zones of these transistors, a metal such as tungsten. The provision of the corresponding metal onto the gate, source or drain zones is usually carried out by means of a metallisation by selective deposition of tungsten using vapour phase chemical deposition.
Such a technique has numerous advantages, the abovementioned selective deposition being easy to perform, implementing the usual operational precautions, by means of appropriate machines such as industrial machines marketed in France by the companies SPECTRUM and TEGAL.
Furthermore, the abovementioned vapour phase deposition produces no uncontrolled consumption of silicon during the operation of the latter.
Tungsten itself has an excellent resistivity value, of the order of 8 .mu..OMEGA..cm, which justifies the choice of the latter so as to produce the electrical connections of the various zones of the transistor or corresponding integrated circuit.
This material also gives a high degree of conformity to the covering of the abovementioned zones, which results in a good mechanical and electrical homogeneity of the corresponding electrical contacts.
However, although the metal/silicon interface constitutes a good diffusion barrier when the chosen deposition metal is tungsten, between the tungsten and silicon molecules, the same does not apply however when this chosen metal is subjected to high temperatures, and this substantially reduces the advantage in such a choice.
The major drawback in the choice of tungsten appears to be the reactivity of this metal with silicon in order to form a tungsten silicide WSi.sub.2 at a temperature above 700.degree. C. The consequence is an increase in the resistivity and the resistance of the connection contact and a consumption in silicon from the junctions of the corresponding zones by creating a rough WSi.sub.2 /Si interface. In particular, it will be noted that recent studies, see Vacuum Technology Industrial Research & Development--March 1983 p 141-147, report a certain stability of the structure Al/W/Si, the latter is however limited to a temperature of the order of 500.degree. C.
Such stability may be sufficient for a single metal integrated circuit, that is to say having a single level of interconnection, but it may not be suitable for modern double metal integrated circuits where the W/Si interface is at 950.degree. C., especially during the flowing stage of the intermetallic dielectric.